X-37B spotted in its classified Orbit, LightSail-A runs into Trouble

May 28, 2015

The semi-secret X-37B space plane has been detected in its classified orbit by a network of satellite trackers in South Africa, confirming that the fourth X-37B mission is using a different mission profile than the three previous missions of the X-37B.

The X-37B OTV-4 mission launched atop an Atlas V 501 rocket blasting off from Cape Canaveral at 15:05 UTC on May 20. As per the usual procedure, only the first four and a half minutes of the mission were shown in the live broadcast covering the burn of the first stage, the separation of the protective payload fairing and the ignition of the Centaur upper stage. Centaur headed into the pre-arranged News Blackout to conceal the initial orbit of the space plane given the semi-secret nature of the mission during which no updates will be provided regarding the status of the spacecraft.

After dropping the X-37B off in its classified orbit, the Centaur Upper Stage went on to conduct an additional burn to raise the apogee of its orbit and significantly increase the inclination before releasing a total of ten CubeSats. LightSail-A, an experimental satellite operated by the Planetary Society to demonstrate propulsion through the use of a large solar sail, was among the CubeSats and a set of orbital elements for it was provided shortly after launch showing an orbit of 355 by 702 Kilometers at an inclination of 55 degrees.

Taking into account the launch time, the known launch azimuth, the reconstructed flight trajectory from the published LightSail TLE and the known deorbit time of Centaur, Ted Molczan, a well known satellite tracker, computed a set of search elements for X-37B, also taking into account the initial orbits of previous missions. These search elements were then available for use by the global satellite tracker community to attempt to spot X-37B in its classified orbit.

OTV-4 was an interesting case since its launch came at a period during which visibility of the craft for most satellite trackers would not begin until several days or weeks into the mission. Observers in South Africa, led by Greg Roberts, had the first chance to begin looking out for X-37B on May 25 on the first visible pass. Roberts was able to observe the X-37B OTV-3 mission just 19 minutes after liftoff and provided observation data for the calculation of the craft’s orbit. With OTV-4 flying to the north-east instead of taking the south-easterly route into orbit, observers in South Africa were unable to watch out for Centaur and X-37B.

Photo: United Launch Alliance

Image: Spaceflight101/JSatTrak

As reported by Roberts on the SeeSat-L mailing list,
he reached out to the satellite tracking community in South Africa to
increase the odds of spotting the vehicle given large areas of the
country are usually covered in clouds this time of year. Imagery of
X-37B was acquired by satellite trackers on May 25 and 26 using
Molczan’s initial search elements as reference.

Observation data delivered to Ted Molczan allowed him to calculate the initial orbit of the X-37B as 312 by 325 Kilometers at an inclination of 37.96 degrees. This confirms that the OTV-4 mission is using a different orbit than the previous X-37B missions that flew at an inclination of 40 to 43 degrees.

Also, the altitude of the initial orbit of the vehicle marks the lowest for X-37B – OTV-1 was delivered to a 403 by 420km orbit, OTV-2 used a similarly low orbit of 317 by 319km, and OTV-3 initially orbited at 345 by 363km. Also noteworthy is the inclination change provided by the Atlas V from the 38° orbit of X-37B to the 55° orbit of the CubeSats, showcasing the performance of the launcher.

The low initial orbit of the craft suggests that OTV-4 may be aiming to demonstrate drag compensation technologies – either using the Hall Effect Thrusters that is known to be on board or another propulsion system like an Electrodeless Lorentz Force Thruster, a project being developed with Department of Defence funding and the goal of developing a propulsion system capable of using a variety of gases as its propellant mass – including air that could be scooped up in extremely low orbits and constantly replenish the propellant aboard the craft to enable satellites to fly on the edge of the atmosphere for an extended period of time which would be particularly useful for optical reconnaissance applications.

If such a system is indeed aboard, it would become evident in orbital data, either in constantly low orbital parameters (drag compensation) or in a changing inclination as it is entirely possible that OTV-4 aims to demonstrate plane-changes using the thruster system to increase the inclination to that used in previous missions.

Entering a relatively low orbit, OTV-4 will have to start orbital maintenance soon, but it is also possible that the craft will raise its orbit over the first few weeks of its long mission that is largely classified. However, in a departure from previous practice, two of the payloads aboard the vehicle have been disclosed to the public.

One is an experimental propulsion system that has been developed by the Air Force Research Laboratory and Space and Missile Systems Center. The system – a Hall Effect thruster – will undergo characterization in orbit to point to any modifications that need to be made to the system before being flown aboard the AEHF (Advanced Extremely High Frequency) satellites that provide secure communications for military application.

The test will involve operation of the thruster over an extended period of time to learn about any degradation that may occur in the space environment through analysis of telemetry gathered from the thruster and data from OTV’s accelerometers, measuring the thrust delivered by the system. Once the thruster begins operating, it can be expected that the orbit of OTV-4 will show a progressive change over extended periods of time since several weeks of thruster activity will be needed to fully characterize the system.

The second publicly known payload hosted by OTV-4 is a materials science experiment operated by NASA. The Materials Exposure and Technology Innovation in Space, METIS, experiment will expose an array of nearly 100 different material samples to the space environment to study the response of the various materials with special focus on degradation as a result of ionizing radiation and metal corrosion by atomic oxygen in Low Earth Orbit.

*File Image* - Photo: US Air Force

X-37B File Image - No Photo of the actual OTV-4 spacecraft has been released

The
experiment is planned to fly for at least 200 days, putting a lower
threshold on the OTV-4 mission duration. METIS materials include
polymer samples, composites and coatings that may find future
application in the construction of spacecraft. A
similar experiment has been in progress aboard the International
Space Station where over 4,000 samples were exposed for a period of a
few months to several years.

With
the initial orbit of X-37B known, satellite trackers will continue
to monitor the vehicle to keep track of potential orbital maneuvers
and possibly identify the timing of Hall Effect thruster operation.
The OTV-4 mission will last for at least two months, but as previous
flights have shown, the vehicle might as well remain in orbit for
over 20 months – depending on the objectives of this mission that are
not being disclosed to the public.

LightSail-A in Trouble

Launched with OTV-4, the LightSail-A mission of the Planetary Society has run into potentially serious trouble. After a successful launch and two days of nominal operations with data being sent back from the 30 by 10 by 10-centimeter CubeSat, the spacecraft fell silent due to a software problem overlooked during ground testing.

The Flight Control Software of the craft logged all telemetry beacons sent back to Earth in a single .csv file. With a beacon transmitted every 15 seconds, this file quickly grew in size until a point was reached when the flight system crashed.

Interestingly, this problem has been known for some time and the manufacturer of the avionics board provided an update to the Flight Software avoiding this particular issue. However, news of that update did not reach the Planetary Society and the LightSail spacecraft operates on the old software without the correction. Teams scrambled to send a patch to the satellite to fix the situation, but the next ground pass with the CalPoly ground station came too late – LightSail-A had fallen silent after its flight computer crashed. The last data packet was received from the vehicle at 21:31 UTC on May 22.

Image: The Planetary Society/Stellar Exploration

The only chance of saving the mission will be a reboot of the Flight Computer – either through a command sent up from the ground or a strike of random luck in the form of an energetic cosmic ray upsetting the system and triggering the reboot. Unfortunately, the satellite was not reacting to numerous attempts of sending a reboot command from the CalPoly and Georgia Tech ground stations.

Without success in commanding the vehicle, it would seem that a cosmic ray hit is the only option for LightSail to come back to life – a relatively common occurrence that comes up every few weeks for CubeSat missions, so there is still some optimism that the satellite will start communicating again for teams to send up a software patch and command a manual deployment of the solar sail. Curiously, LightSail does not include an external watchdog that would automatically reboot the system in case of extended periods of inactivity, a relatively standard piece of equipment, even in CubeSat missions.

ULA Atlas V successfully Launches X-37B Space Plane & CubeSats

May 20, 2015

Photo: United Launch Alliance

A United Launch Alliance Atlas V rocket successfully carried the fourth X-37B mission into orbit on Wednesday, marking the start of a multi-month mission of the semi-classified space plane operated by the United States Air Force. The Atlas V rocket blasted off from Space Launch Complex 41 at Cape Canaveral Air Force Station at 15:05 UTC, climbing into clear skies over the Florida space coast under the power of its two-chamber RD-180 engine.

The first stage operated for a little over four minutes before handing over to the trusted Centaur upper stage that completed its mission without the public watching as the vehicle flew into a pre-arranged News Blackout after second stage ignition was confirmed. Confirmation of a successful launch was provided after X-37B was released into orbit and Centaur went on to complete a secondary mission to release ten CubeSats into orbit after a second main engine burn.

OTV-4 is the fourth mission of the X-37B that made its first flight back in 2010 and has since completed longer and longer missions, its most recent one lasting 22 months. The winged space-plane has been designed to carry payloads into orbit for extended periods of time before returning them by making a fully autonomous re-entry and a landing on a runway.

The
X-37B is 8.9 meters long, has a wingspan of 4.5 meters and a launch
mass around five metric tons featuring a payload bay that can be opened
up to expose payloads to the space environment.

The
X-37B OTV-4 mission flies a series of payloads, including a materials
science experiment operated by NASA to learn about the behavior of
different materials in the harsh space environment to ease the selection
of materials to be used in future spacecraft. Also, the vehicle hosts
an experimental ion thruster that will be tested in an operational
environment before being cleared for use aboard a future spacecraft.
Furthermore, the mission is carrying a series of other experiments that
are not being revealed to the public. As
part of its semi-secret mission, X-37B is launched into a classified
orbit and no details on the progress and possible duration of the
mission are being released.

Also part of this launch were ten CubeSats, carried into orbit aboard an UltraSat deployment mechanism that was to release the spacecraft after the second stage had maneuvered into a different orbit. Part of the satellites is the Planetary Society’s LightSail-A – a first demonstration mission of the technology needed for solar pressure propulsion using a large-area solar sail oriented toward the sun in a way that creates a controllable thrust component. This first mission is only a proof of concept of the satellite systems including the deployment of the large solar sail before a second mission into a higher orbit will demonstrate actual ‘solar sailing’ to evaluate the feasibility of solar pressure propulsion. The other CubeSats delivered to orbit will complete a series of technical demonstrations of various systems such as a webserver in space, small satellite propulsion systems and multi-user communications systems. >>>X-37B Spacecraft Overview>>>Overview of all ten CubeSats launched as part of the AFSPC-05 Mission

Atlas V countdown operations started very early in the morning at Cape Canaveral as the launch team reported to console just before 4a.m. local time to begin the launch checklist starting with communication checks between the various support stations involved in the operation. The Atlas V rocket was powered up around seven hours prior to launch to begin a detailed set of pre-launch checkouts of its various subsystems including the electric system, Propulsion system, Flight Control Systems, Flight Termination System and communications systems. Out at SLC-41, teams were busy for the first several hours of the countdown, closing out the launch vehicle and buttoning up the different ground systems before evacuating the launch area later on to clear the way for tanking.Atlas V entered communications checks inside L-5 hours starting with the C-Band system before the S-Band system underwent testing as well. Teams set up the purge system and applied Nitrogen purge flow at L-3 hours and 40 minutes in preparation for propellant loading.

Photo: United Launch Alliance

At the Morrell Operations Center, Range Controllers reported to console to begin the set up of range instrumentation and start monitoring the clearance of the launch hazard area that came into effect two hours and 20 minutes prior to the planned T-0 time.

The various systems of Atlas V checked out as planned and the Launch Team went into preparations for the propellant loading operation. Countdown clocks held at T-2 hours for the first of two built-in holds in Wednesday’s countdown that gave the launch team the opportunity to catch up with fueling preparations and complete the necessary polls ahead of propellant loading. No hold-ups were identified and all stations provided a GO for tanking operations that commenced as soon as clocks started ticking again after the completion of the hold.

Photo: United Launch Alliance

Heading into tanking operations, the Rocket Propellant 1 Tank of the Common Core Booster first stage that had already been loaded with 94,600 liters of Kerosene on Tuesday, was pressurized to an intermediate pressure before cryogenics were loaded into the Atlas V. Helium bottles on both stages were pressurized and started charging to feed pressurant gas to the tanks during the flight. Next, the Liquid Oxygen ground systems and the oxidizer transfer lines and MLP systems were pressurized and started the chilldown. Fed from a large LOX sphere at SLC-41, the Centaur LOX tank began chilldown just before passing the L-2 hour 20-minute mark followed by the initiation of conditioning on the 1st stage starting around L-2:08. Chilldown of completed to avoid a shock to the metal when coming into contact with the –183°C Liquid Oxygen.LOX flow on Centaur was initiated at L-2 hours and 14 minutes starting in slow fill until the initial portion of the tank was filled when fast fill was initiated to eventually reach the topping stage when the tank passed the 95% mark. CCB oxidizer loading commenced right around L-2 hours and also went through slow and fast fill before reaching topping. Overall, CCB received 185,500 liters of LOX while the Centaur upper stage was filled with 15,700 liters of oxidizer. The last tank to be filled was the Liquid Hydrogen Tank on the Centaur. LH2 loading ops commenced at L-1 hours and 55 minutes when the ground system was pressurized and chilled down ahead of tank chilldown and the start of –253°C LH2 flow to the Centaur stage at L-1 hour and 20 minutes to fill 48,100 liters of fuel into the upper stage.Using its 501 configuration, Atlas V stood 62.2 meters tall on its pad with a diameter of 3.81 meters and a launch mass around 337,300 Kilograms consisting of the standard Common Core Booster and Centaur stack with no Solid Rocket Boosters and the larger version of the Atlas payload fairing featuring a five-meter diameter to accommodate the wingspan of the X-37B space plane.

﻿﻿The Common Core Booster is 32.46 meters tall and holds 284,089 Kilograms of propellants at liftoff to be consumed by a Russian-built two-chamber RD-180 engine that delivers 4,152kN of vacuum thrust. Sitting atop is the Centaur upper stage with its reduced diameter of 3.05 meters connected to the CCB via an Interstage Adapter. 12.68 meters in length, Centaur holds 20,830kg of cryogenics used by a single RL-10C engine to generate 106 Kilonewtons of thrust.

Heading into the last 90 minutes of the countdown, Atlas V started another round of systems testing that included pressurizing hydraulic and pneumatic systems and putting the RD-180 and RL-10 through a series of steering checks. The launcher also repeated communication checks and final open-loop tests on the Flight Termination System were completed. A refined version of the Flight Software was loaded into the redundant Flight Control System of the Atlas V based on the latest measurements of Upper Level Winds. The fault protection system was configured for flight and the RD-180 engine underwent its Fuel Fill Sequence in which a small high-pressure RP-1 tank was filled to be used during ignition to break the membranes of the igniter fluid ampoules holding the pyrophoric igniter that is injected into the gas generator and combustion chambers at engine start.﻿﻿

Photo: United Launch Alliance

Countdown clocks held again at T-4 minutes for the final built-in hold with a planned duration of 30 minutes to accommodate the final preparations of the Atlas V rocket and the X-37B spacecraft for the Automated Countdown Sequence. Going through a number of steps, the X-37B was transferred to internal power and switched to launch mode, executing its flight sequence to be ready for deployment in orbit. The Launch Team verified that Atlas V was fully fueled and completed the final ground systems reconfigurations ahead of terminal countdown.

Polling of all Launch Team Stations showed that everything was a GO – all systems on the launcher and spacecraft were ready, the weather was holding up and the Eastern Range was clear for liftoff. Atlas V headed into its Automated Countdown sequence at 15:01 UTC to initiate the last critical steps to transition to its liftoff configuration.

The first step of the Automated Countdown Sequence was the arming of pyrotechnic systems on the ground at T-3:55 followed by securing of the Liquid Oxygen tank of the Common Core Booster to set up for the pressurization of the CCB tanks to flight pressure that commenced a short time later.

The Flight Termination System was switched to its onboard power source at T-2:45 with arming of the system confirmed twenty seconds later.

At T-2 minutes, Atlas V made its transfer from ground facility power to internal battery power. The launch vehicle’s computers assumed control of the rocket’s systems and executed the final steps of the countdown. Centaur LOX and LH2 tank securing was completed at T-1:50 and T-1:40 to begin the pressurization of all tanks. A final check of bus voltages and hydraulics pressure was completed at T-80 seconds. Final clearance from the Eastern Range was reported at T-60 seconds and all propellant tanks were verified at flight pressure at T-40 seconds. Green board was announced 20 seconds prior to launch.

At T-2.7 seconds, the RD-180 engine came to life when it went through its precisely controlled ignition sequence – injecting pyrophoric TEA into the gas generator and combustion chamber that ignited when coming into contact with LOX, starting the combustion process that allowed the turbopump to reach flight speed with the combustion process sustained by the injection of Kerosene fuel. RD-180 was monitored by computers as it ramped up to 390,200 Kilogram-force of thrust.

Atlas V was sent off at 15:05:00 UTC, the top of its first launch window of the day. Rising from its launch pad, Atlas V lifted off at an initial thrust to weight ratio of 1.16. The rocket balanced in a vertical posture by gimbaling the two nozzles of its RD-180 engine.

Vertical ascent lasted for 18 seconds after which Atlas V started its pitch and roll maneuver to begin aligning itself with its 61° launch azimuth, taking it on a north-easterly departure path – marking the first time X-37B departed Cape Canaveral to the north-east after having previously launched to the south-eastern corridor. Burning 1,150 Kilograms of propellant per second, Atlas V started racing uphill and made its way downrange to depart Florida’s space coast.

Upon completion of the roll maneuver, Atlas V enabled active Propellant Utilization after using a fixed mixture ratio for the initial portion of the ascent. With Propellant Utilization active, the mixture delivered to the engine was precisely controlled to ensure an optimized consumption of propellants.

Atlas V broke the sound barrier just after passing the T+1-minute mark followed by Maximum Dynamic Pressure 89 seconds into the flight. Afterwards, the vehicle switched its Flight Control System to the Zero-Angle of Attack flight mode which controls the attitude of the launcher using a pre-programmed attitude profile that was optimized for the current atmospheric conditions.

Showing rock solid performance, Atlas V continued to fire its RD-180 engine as it embarked on a fast trip across the Atlantic Ocean with the thrust on the engine rising to 422,400 Kilogram-force as the vehicle departed the dense atmosphere. RD-180 finds its origin in the four-chamber RD-170 engine that is the most powerful rocket engine ever built. It is 3.15 meters in diameter and 3.56 meters long weighing 5,480 Kilograms. RD-180 maintains a high-pressure staged combustion cycle employing an Oxygen-rich preburner requiring an exceptionally high chamber pressure of 267 bar.

While the first stage was still powering uphill, the Centaur upper stage made its preparation for the first burn of the RL-10 engine that initiated its in-flight chilldown sequence and Centaur fired a pyrotechnic valve that connected the pressure bottles to the Reaction Control System tanks to ready that system for operation.

Three minutes and 28 seconds after liftoff, Atlas V jettisoned its payload fairing, marking a very early fairing release that can be tolerated by the X-37B given its aerodynamic properties.

Photo: United Launch Alliance

Photo: United Launch Alliance Webcast

The two halves of the fairing were split open using charges so that the fairing halves could rotate outward on hinges before separating from the vehicle and dropping away. Fairing separation was followed by the jettisoning of the Forward Load Reactor. With the fairing gone, the space plane was exposed for the rest of its journey into orbit.

Passing T+4 minutes, the Atlas V rocket started throttling back its RD-180 engine to limit acceleration on the vehicle as it got lighter and lighter when approaching the exhaustion of propellants on the first stage.

Photo: United Launch Alliance Webcast

Photo: United Launch Alliance Webcast

Image: United Launch Alliance

Four minutes and 24 seconds after liftoff, the RD-180 engine was shut down followed six seconds later by the firing of separation pyros to disconnect the first stage from the Centaur upper stage with separation accomplished by eight rertrorockets that were ignited on the first stage that was headed towards a splashdown in the Atlantic Ocean.

Immediately after separation, Centaur purged its reaction control system and pre-started its RL-10C engine. Ignition and full thrust on the engine was confirmed four minutes and 40 seconds after liftoff as Centaur assumed its responsibility of boosting the stack into orbit.

At that point, the mission headed into the customary News Blackout that is implemented to protect the few secrets the X-37B program still maintains such as the target orbit of the vehicle. Based on the previous missions of X-37B, the initial orbit will likely be between 350 and 400 Kilometers in altitude with an inclination of around 40 degrees. The orbital inclination is associated with some uncertainty given this mission’s new launch trajectory on a 61° azimuth.

Photo: United Launch Alliance Webcast

Photo: United Launch Alliance Webcast

The vehicle was to reach the target orbit with a single burn of the Centaur upper stage for X-37B separation taking place less than 20 minutes after launch. Entering orbit, the space plane would begin communications with the ground, start attitude acquisition and after some time, open its payload bay doors and extend its power-generating solar array.

Satellite trackers around the world are already standing by to watch out for the X-37B to determine its precise orbit and start keeping track of the mission.

Image: Boeing Phantom Works

Previous OTV flights were closely watched by the amateur
satellite tracking community that made it possible to follow the
orbital maneuvers of the craft and monitor the progress of the
mission.

After the separation of the X-37B, Centaur was to conduct another main engine burn to raise the apogee of its orbit to the neighborhood of 700 Kilometers and adjust its inclination for the separation of the ten CubeSats. Confirmation of separation of all satellites can be obtained through their UltraSat Deployer, but the health of each individual satellite will be confirmed as it makes its first pass over its operator ground station and therefore may take several hours.

Centaur was to end its flight with a targeted deorbit-burn for destructive re-entry over the Indian Ocean to dispose of the upper stage and avoid leaving it in orbit. Wednesday’s Atlas V mission marked the 636th launch of a vehicle named Atlas since the start of the program back in the early days of America’s space endeavors in 1957. It was the 225th mission of the Centaur Upper stage, the 202nd atop an Atlas booster. Atlas V made its 54th mission on Wednesday, the sixth in the 501 configuration. ULA’s next mission is on the books for July 14 when an Atlas V 401 will loft the next Global Positioning Satellite into orbit.

Atlas V rolls to Launch Pad for semi-secret X-37B Launch

May 19, 2015

An Atlas V 501 rocket carrying the X-37B space plane and a series of CubeSats made its way to the Launch Pad at Space Launch Complex 41 of Cape Canaveral Air Force Station on Tuesday in preparation for liftoff on Wednesday to mark the start of the fourth flight of the semi-classified X-37B vehicle on a multi-month mission to Lower Earth Orbit. Liftoff is set for a four-hour launch period starting at 14:45 UTC and the mission includes the usual secrecy as no target orbit for X-37B is disclosed to the public, leaving it up to satellite trackers around the world to track the progress of the OTV-4 mission. Wednesday's launch will head into the customary news blackout after the ignition of the second stage.

United Launch Alliance conducted the Launch Readiness Review for the OTV-4 mission on Monday as a final look at the status of all launch vehicle systems and required systems on the ground to make sure everything was ready to support the third Atlas V launch of the year after the workhorse already lofted a MUOS satellite in January and delivered NASA’s four ﻿MMS satellites in﻿to a high orbit in March.

Photo: United Launch Alliance

No show-stoppers were found and the Atlas V rocket was cleared for the rollout to the launch pad.

Sitting
atop the Mobile Launch Platform, Atlas V 501 completed the half-hour
trip from the Vertical Integration Facility to the launch pad on Tuesday
morning, local time. Arriving at the launch pad, the vehicle was
carefully centered in position so that teams could start the multi-hour
process of connecting the vehicle to power, data, propellant,
pressurant, and purge umbilicals. Later in the day, the trackmobiles
used to move the MLP are disconnected and removed from the pad and the
Atlas V first stage is filled with 94,600 liters of Rocket Propellant 1.
Atlas V will be buttoned up for its overnight stay at the pad before
teams will return in the very early hours on Wednesday to initiate
countdown operations, starting with the Launch Team reporting to console
seven an a half hour prior to the planned T-0 time.

X-37B
requires the Atlas V to launch in its 501 configuration, hosting a
larger payload fairing to accommodate the 4.5-meter wing span of the
space plane.

In its 501 configuration, Atlas V stands 62.2 meters tall, has a diameter of 3.81 meters and a launch mass of 337,300 Kilograms. It can deliver payloads up to 8,123 Kilograms to Low Earth Orbit, leaving some margin when lofting the five metric-ton X-37B craft. The first stage of Atlas V is known as the Common Core Booster that stands 32.46 meters tall and holds 284,089 Kilograms of Rocket Propellant 1 and Liquid Oxygen for consumption by a Russian-built RD-180 two-chamber engine that delivers a total sea level thrust of 3,827 Kilonewtons.>>>Atlas V 501 Overview

Sitting atop the first stage is the trusted Centaur Upper Stage that has been around for decades, this being its 225th mission. Centaur is 3.05 meters in diameter and 12. 68 meters long, holding 20,830kg of Liquid Oxygen and Liquid Hydrogen that are used by a single RL-10C engine to generate 106kN of vacuum thrust. Centaur can perform multiple burns to target a variety of orbital trajectories.

Photo: United Launch Alliance

Meteorologists continue to predict a 60% chance of favorable weather conditions for Wednesday’s launch attempt. It is expected that conditions will be best at the opening of the window before sea breeze conditions set in and bring clouds and thunderstorms to Cape Canaveral, leading to violations of launch weather criteria. Primary concerns include cumulus and anvil clouds, surface electric fields and lightning. In the event of a 24-hour delay, conditions will worsen considerably with only a 30% chance of cooperative weather.

Ahead of the countdown, technicians will already be busy at the pad, completing final hands-on work and closing out the Vertical Integration Facility, pad facilities and the Atlas V launcher. The first step completed at T-6 Hours 20 Minutes is the activation of the Atlas V rocket.

Following the activation of the launcher, teams begin a series of checkouts of the electrical system of the rocket. Meanwhile, at the launch pad, technicians complete final hands-on work. While that is in progress, the Launch Team puts the Atlas V through a series of communications checks on its S- and C-Band Systems in addition to other tests.

Flight Termination System testing is also completed and the Nitrogen Purge flow on the vehicle is initiated. By L-3 hours, the launch pad is cleared by all personnel.

At T-2 Hours, the countdown enters a 30-minute built-in hold during which teams perform the fueling pre-task briefing and the GO/No GO Poll for propellant loading. As soon as the countdown resumes at T-2 Hours, propellant loading operations start. The complex procedure to load the two stages of the rocket with cryogenics begins with the chilldown of ground support equipment and transfer lines and tanks chilldown on the Liquid Oxygen side.

Once Centaur is into propellant loading, the large Liquid Oxygen tank of the Common Core Booster also starts fueling. LOX load on the CCB also moves through the three steps, slow-fill, fast-fill and topping. The Common Core Booster is loaded with Rocket Propellant 1 (refined Kerosene) ahead of the launch countdown.

The final tank to be loaded during the countdown is the Liquid Hydrogen Tank of the upper stage that also goes through the usual steps. Centaur is loaded with a total of 48,100 liters of -253-degree Celsius LH2 fuel. When clocks reach T-4 Minutes, the countdown enters its final built-in hold. This hold can be extended in case of technical issues or uncooperative weather. During the hold, the launch team receives a final weather briefing, the spacecraft is switched to internal power and teams perform the GO/No GO Poll for the Terminal Countdown.

As clocks start ticking down from T-4 Minutes, final vehicle configurations such as ordnance arming, flight termination system arming, propellant tank pressurization, transfer to internal power, and flight control system reconfigurations will be made as part of the Automated Sequence to place the vehicle in its launch configuration.

At T-2.7 seconds, the massive two-chamber RD-180 main engine of the Common Core Booster ignites and soars up to its full liftoff thrust of 390,250 Kilograms. Engine start-up is closely monitored by flight computers to make sure it reaches operational conditions before the launcher is committed to flight.

Lifting off with an initial thrust to weight ratio of 1.16, Atlas V will make a slow vertical climb, balancing itself in an upright posture by gimbaling the two nozzles of the RD-180 engine. Vertical ascent will take 18.3 seconds before Atlas V begins its pitch and roll maneuver to align itself with its 61-degree launch azimuth to begin flying down a precisely planned trajectory, headed towards a classified orbit.

At the completion of the roll maneuver, Atlas V will switch to closed loop Propellant Utilization after initially having the engine operate at a fixed mixture ratio. With propellant utilization active, Atlas V will precisely control the propellant mixture provided to the engine to ensure an optimized consumption of propellants.

After passing the T+1-minute mark, Atlas V will pass the speed of sound before encountering Maximum Dynamic Pressure 88.8 seconds into the mission. RD-180 will be firing at full throttle throughout most of the first stage burn, consuming 1,150 Kilograms of RP-1 and LOX each second of powered flight.

Photo: United Launch Alliance (File Image)

After passing MaxQ, Atlas V will transition the Flight Control System to the Zero-Angle of Attack flight mode which controls the attitude of the launcher using a pre-programmed attitude profile that was computed before launch based on measured conditions in the upper atmosphere.

While the first stage is burning, the Centaur upper stage will prepare for its burn by starting the in-flight chilldown of the RL-10C engine and firing a pyro valve to initiate the pressurization of the hydrazine attitude control system of Centaur. Departing the dense layers of the atmosphere, thrust of the first stage will increase to 415,200 Kilogram force.

At T+3 minutes and 28 seconds Atlas V can jettison its protective payload fairing since aerodynamic forces can no longer cause harm to the launch vehicle. This fairing separation time is much earlier in the flight plan than for usual satellite launches given the aerodynamic capabilities of the X-37B that could be launched without a fairing altogether. However, modeling the dynamic launch environments of X-37B atop Atlas V without fairing would require a complex set of analyses and it was therefore decided to keep the well-known flight dynamics with the fairing for the critical portion of atmospheric flight given the surplus of performance of Atlas V that can afford to lift the additional mass of the fairing for the first minutes of flight and still deliver X-37B to its target orbit.

Around T+4 minutes into the flight, the main engine will begin a gradual throttle-back to limit acceleration on the launch vehicle to 5Gs as the rocket gets lighter and lighter, approaching the shutdown of its first stage. Cutoff of the RD-180 is expected four minutes and 23.5 seconds after launch.

Six seconds after BECO, the pyrotechnic stage separation system is fired and the Common Core Booster ignites eight small retrorockets that push the spent stage away from Centaur.

Immediately after separation, Centaur will purge its Reaction Control System and pre-start the engine on LOX and LH2 followed by igniter spark and engine ignition at T+4 minutes and 39.5 seconds into the flight. This mission is using the RL-10C engine that is becoming the standard engine of choice for Atlas V’s Centaur upper stage to eventually also be used on the Delta Cryogenic Second Stage to eliminate cost by replacing two different, but related, engine designs with one common engine. RL-10C delivers a vacuum thrust of 106 Kilonewtons, slightly more than the RL-10A-4-2 and a little less than the RL-10B-2 with its huge nozzle. The engine achieves a specific impulse of 448.5 seconds. RL-10C measures 1.44 meters in diameter and 2.22 meters in length with a total mass of 190 Kilograms.

After the ignition of the Centaur Upper Stage is confirmed, the mission will head into the typical news blackout of X-37B flights to keep the target orbit of the vehicle secret -- A secret that will last only for a couple of days as satellite trackers around the world will be on the look-out to spot the X-37B in orbit to keep tabs on its maneuvers and the progress of the mission.

Image: Boeing Phantom Works

Sticking to a nominal flight profile, Centaur will only need one burn to reach the target orbit of the X-37B that will likely be somewhere between 350 and 400 Kilometers in altitude based on the previous three missions of the semi-classified vehicle. The orbital inclination of the OTV-4 mission is another story because this launch is the first to use a 61-degree launch azimuth to the north-east. The previous OTV missions departed Cape Canaveral on a launch azimuth of around 110 degrees and headed to orbital inclinations of 40 to 43.5 degrees, by taking advantage of Centaur’s performance, burning out of plane to change the inclination. It can be assumed that this launch will also follow the deviation from a straight-line delivery into orbit and include an inclination change of some magnitude. The orbital inclination of the X-37B will be revealed once satellite trackers can spot the vehicle.

Following the completion of the primary mission that is to deliver the X-37B, the Centaur Upper Stage is set for one or two engine burns to reach the target orbit of the CubeSats that are being carried aboard an UltraSat deployment mechanism. The various payload operators have not revealed exact orbital parameters, often citing an ‘inclination near 50°’ and and orbit of around 350-390 by 700 Kilometers. This would require Centaur to make one burn post OTV separation to increase the apogee and adjust the inclination prior to the sequential release of the ten CubeSats.

Centaur will close out its mission by conducting a targeted deorbit burn for destructive re-entry over a remote location above the Indian Ocean.

After the launch of this mission, Satellite Trackers around the world will be watching possible Low Earth Orbit slots to identify the vehicle and keep track of it throughout its mission. For the previous flights, satellite trackers were able to spot X-37B within days and keep track of its orbital maneuvers throughout the mission. Ted Molczan posted OTV-4 search elements based on previous missions.

Fourth X-37B Mission set for Liftoff atop Atlas V this Week

May 18, 2015

Photo: United Launch Alliance

The semi-classified X-37B Space Plane is ready for its next multi-month flight into orbit with launch atop an Atlas V 501 rocket planned on Wednesday during a four-hour window opening at 14:45 UTC.

Unlike the previous three missions of the X-37B, this mission is not shrouded in complete secrecy since some details on the payloads carried by the vehicle have been published by their operators. In addition to OTV-4, the Atlas V rocket is also carrying a number of CubeSats to be deployed after the release of the X-37B from an UltraSat deployer installed on the Centaur Upper Stage of the Atlas V rocket.

Preparations for this mission started back in late March when the first stage Common Core Booster was installed atop the Atlas V Launch Table inside the Vertical Integration Facility at Space Launch Complex 41 of Cape Canaveral Air Force Station. The next step was the installation of the vehicle’s Centaur Upper Stage along with its Interstage Adapter.

The
X-37B spacecraft to fly this mission was processed for launch over the
past months, being fitted with its payloads and receiving propellants
for its mission into space that will likely last several months,
however, details such as exact mission duration and operational orbit
are not disclosed to the public for X-37B flights.

Originally,
the mission was targeting a May 6 launch date, but was pushed by two
weeks in April on request of the payload side. On May 7, the X-37B –
encapsulated in the five-meter version of the Atlas V payload fairing –
was installed atop its launch vehicle marking the completion of the
lengthy integration process and signaling the start of integrated
testing between the launch vehicle and payload that also includes
mission simulation tests and countdown rehearsals to ensure the
integrated system is ready to support the mission.

The X-37B,
originally a project of NASA, Boeing and the US Air Force, was
transferred to become a fully military-operated project in 2004 and
entered an area of semi-classification to a point where some details on
the vehicle and its missions are being shared and others are being kept
secret.

The solar-powered spacecraft measures 8.9 meters in length as has a wingspan of 4.5 meters with a nominal launch mass on the order of five metric tons. A small payload bay is opened up in space exposing any experimental payloads the craft may be carrying to the space environment for testing ahead of a return to Earth towards a fully automatic landing on a runway.

X-37B is not new to riding into space atop Atlas V, having been launched on all of its previous missions atop the trusted launch vehicle. OTV-1 was the maiden voyage of X-37B and launched in April 2010, entering a classified orbit that was later revealed by satellite trackers, spotting the vehicle flying over 400 Kilometers above the Earth. The spacecraft showed frequent orbital maneuvers, lowering its orbit toward the end to the mission to under 300 Kilometers, setting up a landing at Vandenberg Air Force Base after 224 days in orbit.

A second X-37B flew the OTV-2 mission that lasted 469 days from March 2011 to June 2012, passing the specified in-orbit life of 270 days for which X-37B was conceptualized. The first X-37B vehicle again headed into orbit in December 2012 for the program’s longest flight to date, returning to Vandenberg in October 2014 after 22 months in orbit.

On its past three flights, X-37B’s payloads were not revealed to the public. For OTV-4, at least some of the experiments carried by the space plane have been disclosed by their operators.

One is an experimental propulsion system that has been developed by the Air Force Research Laboratory and Space and Missile Systems Center. The system – a Hall Effect thruster – will undergo characterization in orbit to point to any modifications that need to be made to the system before being flown aboard the AEHF (Advanced Extremely High Frequency) satellites that provide secure communications for military application.

Photo: United Launch Alliance

The test will involve operation of the thruster over an extended period of time to learn about any degradation that may occur in the space environment through analysis of telemetry gathered from the thruster and data from OTV’s accelerometers, measuring the thrust delivered by the system.

Photo: United Launch Alliance

The second publicly known payload hosted by OTV-4 is a materials science experiment operated by NASA. The Materials Exposure and Technology Innovation in Space, METIS, experiment will expose an array of nearly 100 different material samples to the space environment to study the response of the various materials with special focus on degradation as a result of ionizing radiation and metal corrosion by atomic oxygen in Low Earth Orbit.

The experiment is planned to fly for at least 200 days, putting a lower threshold on the OTV-4 mission duration. METIS materials include polymer samples, composites and coatings that may find future application in the construction of spacecraft.

A similar experiment has been in progress aboard the International Space Station where over 4,000 samples were exposed for a period of a few months to several years.

“By exposing materials to space and returning the samples to Earth, we gain valuable data about how the materials hold up in the environment in which they will have to operate,” said Miria Finckenor, the co-investigator on the MISSE experiment and principal investigator for METIS at NASA’s Marshall Space Flight Center in Huntsville, Alabama. “Spacecraft designers can use this information to choose the best material for specific applications, such as thermal protection or antennas or any other space hardware.”

Meteorologists are predicting 60% odds of favorable weather conditions for Wednesday’s launch window. According to forecast models, conditions will be best at the opening of the window before deteriorating later on due to sea breeze conditions that will bring showers and thunderstorms. Primary concerns include violations of the Cumulus Cloud Rule, surface electric fields, anvil clouds and lightning. Given the semi-secret nature of X-37B, the launch broadcast provided by United Launch Alliance will end after the ignition of the Centaur Upper Stage is confirmed, about four and a half minutes after launch. Centaur will then head into a classified orbit for the release of X-37B followed by post-separation maneuvers for the deployment of the CubeSats that are part of this mission.

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